Epidermal bladder cells play a role in water retention in quinoa leaves

Quinoa, a pseudocereal and leafy vegetable native to South America, is highly nutritious and can grow in harsh environments. One of the most prominent morphological features of quinoa is that the above-ground portion is covered with a layer of epidermal bladder cells (EBCs), and the role of EBCs in quinoa's high stress tolerance is of interest. Recent studies have shown that two WD40-repeat proteins, Reduced number of EBC (REBC) and REBC-like1, are required for EBC formation and that EBCs contribute defense mechanisms against biotic stress rather than abiotic stress. However, the role of EBCs in drought stress tolerance remains controversial due to the pleiotropic effects of these genes, including their impact on plant growth. Here, we show that REBC and REBC-like1 mediate water retention in detached quinoa leaves. Using a virus-induced gene silencing (VIGS) system, we found that downregulation of both REBC and REBC-like1 had no apparent effect on plant growth, but reduced the number of EBCs in both lowland and highland quinoa lines. Further, downregulation of both genes increased water loss in detached leaves of quinoa plants, supporting the notion that EBCs mediate water retention in quinoa leaves. Interestingly, we found higher EBC density in the southern highland lines grown in drier areas. Thus, we demonstrate that the effective use of VIGS in the analysis of genes with pleiotropic effects allows analyses that were difficult to perform using mutants alone, and that unlike mutants, functional genomics studies of quinoa can be easily performed in various lines using VIGS.